Crispin CR-AR5.5" Air Release Valve Crispin systems under pressure can be vented of accumulating air with the use of Pressure Air Release Valves. These should be mounted on the system at all high points, and downstream from these points where the velocity of the liquid carries the air or gas slightly beyond the crest. On lines with little gradient, valves should be placed every half mile or so, at the discretion of the engineer. Similar in many ways to the Midget Series, the AR Series comes with one orifice rated for 300 PSIG. A more economical option, replacement parts are not offered.